Thermal and Crystallographic Properties of Tetra-n-butylammonium Bromide + Tetra-n-butylammonium Chloride Mixed Semiclathrate Hydrates

Abstract

The thermal and crystallographic properties of tetra-n-butylammonium bromide + tetra-n-butylammonium chloride (TBAB + TBAC) mixed semiclathrate hydrates prepared from mixed aqueous solutions were investigated using phase equilibrium measurements, differential scanning calorimetry (DSC), and powder X-ray diffraction. The equilibrium temperatures gradually vary with both x guest {i.e., the mole fraction of guests to (guests + water)} and x TBAB {i.e., TBAB to (TBAB + TBAC)}. The maximum equilibrium temperatures for each concentration changed from (x TBAB = 0.4 to 0) and were observed at x TBAB = 0 below x guest = 0.012. The dissociation enthalpies of tetragonal mixed hydrates are between those of the pure hydrates. In the tetragonal pure and mixed hydrates, these results indicate that the thermal stabilities are dependent upon the increase of hydration number by the relaxation of crystal distortion with decreasing x guest and x TBAB. In orthorhombic systems, a single endothermic DSC peak is split to a higher temperature from x TBAB = (1.0 to 0.6) at x guest = 0.006, and the dissociation enthalpies gradually increase with decreasing x TBAB. The orthorhombic (TBAB + TBAC) mixed hydrates are formed as eutectic crystals with orthorhombic TBAB hydrate and that they are more thermally stable than the TBAB hydrate.

Promoting Effect of Ultra-Fine Bubbles on CO2 Hydrate Formation

“…However, gas hydrates have unique properties, such as a large gas storage capacity; therefore, they are a promising medium for transporting and storing gases [5][6][7]. Additionally, gas hydrates, or more generally clathrate hydrates, have attracted attention as refrigerants owing to their melting points that are higher than that of ice [8][9][10][11], as they have a large latent heat similar to ice. Research on gas hydrate utilization has increased in recent years, and such research has focused on efficient gas hydrates formation.…”

Effect of Adding Potassium Chloride on Tetra-n-butyl Ammonium Chloride Semiclathrate Thermal Stability at Atmospheric Pressure

“…This halide then has some degree of Coulombic interaction with this nitrogen ion but also forms ion-dipole bonds with the adjacent water molecules which are stronger than the dipole−dipole bonds of the water molecules found in the analogous clathrate water cages. 6,14 This then causes the resulting semiclathrate molecule to be more thermally stable than its clathrate counterpart. In fact, the melting point of these semiclathrates is found to be above the melting point of pure water at atmospheric pressure.…”

Effects of multiwalled carbon nanotubes on CH4 hydrate in the presence of tetra-n-butyl ammonium bromide

“…The PXRD patterns of all the hydrate samples are consistent with orthorhombic Pmma structures. 53,54 The peaks at 2 θ = 7.11°, 8.57°, 11.1°, 16.4°, 17.2°, and 18.4° were assigned to Miller indices ( h k l ) of 010, 200, 210, 220, 202, and 401, respectively. In the PXRD pattern of pristine MWCNTs, the peaks at 2 θ = 25.85° and 43.43° were assigned to the Miller indices ( h k l ) of 002 and 100.…”